Logistics Officers on Submarines

I was always under the impression that a Logistics Officer could be REQUIRED to serve on a submarine (maybe for one draft), yet now I see LO (Submariner) on the RN website, meaning you have to join specifically for that and only ever go on submarines when at sea (I assume). Could somebody clear this up for me as I am now a bit confused. Many thanks!
Hello mate, as I understand it you can join up as a Logs(SM) and you will do a short draft on a skimmer as part of your phase 2 training, then do a shore draft, then you do your 'main' sea draft on a boat. Then back inboard for a while. If you climb the ladder enough you may go back to sea on a skimmer as a task group pusser.
So if you join up as a logs (SM) you'll go to sea as pusser of a submarine.